1. Field of the Invention
This invention relates to a novel polyurethane polymer, especially a low molecular weight polyurethane polymer, which is the reaction product of a diisocyanate and a particular polyol adduct. This invention is concerned with lubricating oil compositions containing the novel polyurethane polymer as a dispersant therein. More especially, this invention is directed to improving the dispersancy of neopentyl polyol derivatives in lubricating oil compositions.
2. Discussion of the Prior Art
In U.S. Pat. No. 3,281,359 to Oberender et al, the disclosure of which is hereby specifically incorporated herein by reference, there are disclosed new neopentyl polyol derivatives useful as detergent/dispersants in lubricating oils, particularly petroleum lubricating oils. These neopentyl polyols are formed by a particular sequence of steps involving the initial formation of a polyolefin-P.sub.2 S.sub.5 reaction product. That reaction product is thereafter treated with steam at temperatures, say, of 100.degree. to 260.degree. C. to form inorganic phosphorus acids which are removed. The product is also treated with methanol to effect extraction of undesired components to leave a hydrolyzed polyolefin-P.sub.2 S.sub.5 reaction product which is substantially free of inorganic phosphorus acid. That product is thereafter treated with a neopentyl polyol of the formula ##STR1## wherein R' and R" are members from the group consisting of alkyl and alkylol of from 1 to 20 carbon atoms at temperatures between about 180.degree. and 220.degree. C. in a mole ratio of neopentyl polyol to hydrolyzed reaction product of between about 0.33:1 and 2:1. The resultant product is believed to be primarily a complex mixture of hydrocarbon phosphorus acid monoesters, diesters, polyesters, cyclic esters and anhydrides. The hydroxyl number of the resultant product is usually within the range of 5 to 350, preferably 20 to 80. This product is an effective detergent/dispersant for lubricating oils, both of the hydrocarbon mineral oil type and the synthetic hydrocarbon, ester, or ether type.
It has become desirable, however, to improve the dispersant properties of this neopentyl polyol derivative so that the same is rendered more efficient in reducing the formation of deposits in gasoline and in diesel engine applications. It has become desirable, therefore, to provide an improved lubricating oil composition having as a detergent/dispersant a neopentyl polyol derivative-based composition of improved dispersancy.